System.TypeInitializationException: The type initializer for 'System.Net.Http.CurlHandler' threw an exception. ---> System.TypeInitializationException: The type initializer for 'Http' threw an exception. ---> System.TypeInitializationException: The type initializer for 'HttpInitializer' threw an exception. ---> System.DllNotFoundException: Unable to load DLL 'System.Net.Http.Native': The specified module or one of its dependencies could not be found.
(Exception from HRESULT: 0x8007007E)
at Interop.Http.GetSslVersionDescription()
at Interop.HttpInitializer..cctor()
--- End of inner exception stack trace ---
at Interop.Http..cctor()
--- End of inner exception stack trace ---
at Interop.Http.GetSupportedFeatures()
at System.Net.Http.CurlHandler..cctor()
--- End of inner exception stack trace ---
at System.Net.Http.CurlHandler..ctor()
at System.Net.Http.HttpClientHandler..ctor()
at Octopus.Client.OctopusAsyncClient..ctor(OctopusServerEndpoint serverEndpoint, OctopusClientOptions options, Boolean addCertificateCallback) in Z:\buildAgent\workDir\52d4a5804c7de8e\source\Octopus.Client\OctopusAsyncClient.cs:line 45
at Octopus.Client.OctopusAsyncClient.<Create>d__12.MoveNext() in Z:\buildAgent\workDir\52d4a5804c7de8e\source\Octopus.Client\OctopusAsyncClient.cs:line 131
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Octopus.Client.OctopusAsyncClient.<Create>d__11.MoveNext() in Z:\buildAgent\workDir\52d4a5804c7de8e\source\Octopus.Client\OctopusAsyncClient.cs:line 116
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Octopus.Cli.Commands.ApiCommand.<Execute>d__31.MoveNext() in Z:\buildAgent\workDir\52d4a5804c7de8e\source\Octo\Commands\ApiCommand.cs:line 97
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Octopus.Cli.Program.Run(String[] args) in Z:\buildAgent\workDir\52d4a5804c7de8e\source\Octo\Program.cs:line 47
Exit code: -3

Thanks for the response. In the end I actually found one of your api example codes using Ruby and I built on that to create my own CLI tool to create releases and deploy.
My build tool is in ruby anyway so now I don't need to shell out. Happy days. :)
It's great that all functionality is available on the api.